Who Sets the Strategy?
Traditionally, architecture is handed down, created before application development begins, by a team that has more power in the organization than the application development team. But it doesn't have to be that way. That way doesn't usually work very well.
Strategic design, by definition, must apply across the project. There are many ways to organize a project, and I don't want to be too prescriptive. However, for any decision-making process to be effective, some fundamentals are required.
First, let's take a quick look at two styles that I've seen provide some value in practice (thus ignoring the old "wisdom-from-on-high" style).
Emergent Structure from Application Development
A self-disciplined team made up of very good communicators can operate without central authority and follow EVOLVING ORDER to arrive at a shared set of principles, so that order grows organically, not by fiat.
This is the typical model for an Extreme Programming team. In theory, the structure may emerge completely spontaneously from the insight of any programming pair. More often, having an individual or a subset of the team with some oversight responsibility for large-scale structure helps keep the structure unified. This approach works well particularly if such an informal leader is a hands-on developer—an arbiter and communicator, and not the sole source of ideas. On the Extreme Programming teams I have seen, such strategic design leadership seems to have emerged spontaneously, often in the person of the coach. Whoever this natural leader is, he or she is still a member of the development team. It follows that the development team must have at least a few people of the caliber to make design decisions that are going to affect the whole project.
When a large-scale structure spans multiple teams, closely affiliated teams may begin to collaborate informally. In such a situation, each application team still makes the discoveries that lead to the idea for a large-scale structure, but then particular options are discussed by the informal committee, made up of representatives of the various teams. After assessing the impact of the design, participants may decide to adopt it, modify it, or leave it on the table. The teams attempt to move together in this loose affiliation. This arrangement can work when there are relatively few teams, when they are all committed to coordinating with each other, when their design capabilities are comparable, and when their structural needs are similar enough to be met by a single large-scale structure.
A Customer Focused Architecture Team
When a strategy will be shared among several teams, some centralization of decision making does seem attractive. The failed model of the ivory tower architect is not the only possibility. An architecture team can act as a peer with various application teams, helping to coordinate and harmonize their large-scale structures as well as BOUNDED CONTEXT boundaries and other cross-team technical issues. To be useful in this, they must have a mind set that emphasizes application development.
On an organization chart, this team may look just like the traditional architecture team, but it is actually different in every activity. Team members are true collaborators with development, discovering patterns along with the developers, experimenting with various teams to reach distillations, and getting their hands dirty.
I have seen this scenario a couple of times, when a project ends up with a lead architect who does most of the things on the following list.